1,23-Triazoles 1.2.4- triazin-3 -ones

Ring contraction reaction of the benzthiazolo[2,3-f][l,2,4]triazin-one derivative 95 has been reported by Kuberkar et al. <2005JCM632> (Scheme 13). This compound when heated in aqueous sodium hydroxide underwent ring opening and a subsequent ring closure to result in formation of the fused [l,2,4]triazole ring system 96 in good yield (60%). 

A special approach to [l,2,4]triazolo[3,2-c][l,2,4]triazine derivatives is the transformation of 3-diazo[l,2,4]triazoles, easily available by diazotation of aminotriazoles. These compounds already contain the five nitrogen atoms in the correct sequence in order to form the desired bicyclic ring system and, thus, their reaction with proper bifunctional reagents can give rise the cyclized products in one single step. Such transformations are collected in Scheme 50. 

Triazines are well-known compounds with high thermal stability and higher EA than 1,3,4-oxadiazoles (PBD) and 1,2,4-triazoles (TAZ, 92). Schmidt et al. studied a series of dimeric 1,3,5-triazine ethers for application as ETMs for OLEDs [150], However, despite their high EA, the efficiency of the OLEDs improved only modestly. One possible explanation is due to their rather poor electron mobilities. 

When the synthesis of a heterocyclic system containing a diazole fused onto l,2,3-triazin-4-one (e.g., imidazo[4,5-i [l,2,3]tnazin-4-one (Section 10.13.9.1.l(i)) and pyrazolo[3,4-rf [l,2,3]triazin-4-one (Section 10.13.9.1.1(ii))) or 1,2,3-triazole fused onto pyrimidin-4(7)-(di)one (e.g., [l,2,3]triazolo[4,5-rf pyrimidin-4(7)-(di)one (Section 10.13.9.1.l(iv))) is required, the synthesis of the six-membered ring is the most reliable method. There are several recent accounts of six-membered annulations onto 1,2,3-triazoles to give [l,2,3]triazolo[4,5-r/ pyrimidines (Section 10.13.9.1.l(iv)), which are valuable alternatives to 1,2,3-triazole annulation using nitrosation techniques <1996CHEC-II(7)489>. 

Amino-l,2,4-triazines (86) react with phenylhydrazine to afford 2-phenyl-l,2,3-triazoles (135) (60MI21900). 3-Thioxo-l,2,4-triazin-5-ones (76) are transformed into 1,2,4-triazole-3-thiones (136) by treatment with sodium methoxide (72BSF1511). Treatment of compound (137) with acetic anhydride in the presence of sulfuric acid led to the isolation of the pyrazole (138) (10JA1499). 

The reaction of l,2,4-triazin-3-ones (141) with hydroxylamine-O-sulfonic acid, chloroamine and sodium hypochlorite has been studied by Rees and coworkers. In the first case imidazolinones (142) were obtained, while in the two other cases 1-,2,3-triazoles (143) were isolated (73JCS(Pl)545). Similarly, treatment of l,2,4-benzotriazin-3-one (144) with chloroamine or lead tetraacetate led to the isolation of benzotriazole (146a) or 1-acetylbenzotriazole (146b), while (144) was converted into benzimidazolinone (145) by hydroxylamine-O-sulfonic acid <73JCS(Pi)545). 

Irradiation of 1,2,4-triazine 4-oxides (124) led to the deoxygenated products, and also, when position 5 was unsubstituted, to 1,2,4-triazoles (364) (76LA153). 4-Amino-l,2,4-triazin-5-ones (365) are photochemically deaminated. This has been demonstrated, in particular, with the 6-r-butyl-3-methylthio compound (8) which is used as a herbicide... 

This year, following a consultation exercise involving members of the Editorial Board, and partly in the interest of getting the Volume published as soon as possible after the end of the year being reviewed, the Index is less comprehensive than formerly. It now includes only systematic heterocyclic ring system names. Thus, wherever a pyrrole is discussed, that would be indexed under pyrroles wherever pyrido[3,4-i]indoles are mentioned an indexed entry under that name will be found similarly aceanthryleno[l,2-e][l,2,4]triazines , azirines , 2f/-pyran-2-ones , 1,2,4-triazoles etc. etc. are listed. But, subjects like 4-ethyl-5-methylpyrrole , 5-acylazirines , 6-alkyl-2//-pyran-2-ones , 3-alkylamino-l,2,4-triazoles , are not listed as such in the Index. Diels-Alder reaction or Fleck coupling etc., are also not indexed. 

Aza-l,3-dienes react with diazenedicarboxylates and 4-phenyl-3ff-l,2,4-triazole-3,5(4//)-dione to afford in good yield, l,2,3,6-tetrahydro-l,2,4-triazines 14 and 15, respectively. The relative configuration of the substituents at C-3 and C-6 of one product derived from diethyl diazenedicarboxylate was ascertained by X-ray analysis32. 

Reaction of 1,2,4-triazol-4-ylamidines (473) with diethyl carbonate in the presence of sodium ethoxyethoxide led (70JPR669) to intermediate 474 which, upon cyclization, gave the l,2,4-triazolo[3,4-/]l,2,4-triazino-8-ones (475). Kurasawa and his group (85JHC1715) reported that the reaction of 3-(a-hydroxyimino-4-amino-5-methyl-4//-l,2,4-triazol-3-ylmethyl)2-oxo-l,2-dihydroquinoxaline (476) with orthoesters and iron powder in acetic acid gave l,2,4-triazolo[3,4-/]l,2,4-triazines 480 and its 7,8-dihydro isomers 479. 

One route to these compounds is the reaction of 3-amino-1,2,4-triazoles (312) with dicyanodiamide (485) to yield (49USP2473797 53JOC1610) 5,1-diamino-l,2,4-triazolo[4,3-a]l,3,5-triazines (486). The 1,3,5-triazine ring of 7-methoxy-3-phenyl-l,2,4-triazolo[4,3-a] 1,3,5-triazine (489) was formed (70T3357) by the direct cyclocondensation of 0-methyl-N-(5-phenyl-l,2,4-triazol-3-yl)urea (488) with methyl diethoxyacetate (487) or triethyl orthoformate. 3,5,7-Triamino-1,2,4-triazolo[4,3-a] 1,3,5-triazine (490) was prepared (53JOC1610 63ZOB1355) in one step by the reaction of two equivalents of dicyanodiamide (485) with one equivalent of hydrazine dihydrochloride. 

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